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Determination of soluble salts in soil samples from Cyprus

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Outline

Estimates of Reproducibility, Limits of Detection (LOD) and Limits of Quantification (LOQ)

Distributions of Fluorides

Distributions of Chlorides

Distributions of Nitrates

Distributions of Sulfates

Conclusions

Introduction

Soil comprises the loose top layer of our planet's crust and contains a mixture of rock particles, organic matter, bacteria, air and water.

Minerals, nutrients

Ions in solution

Heat, cold, wind,

rain, hail, ice

Oxides of iron & alumina

Spontaneous

weathering

Frost

Silica

Mechanical

weathering

Clays

Parent material

Fine parent

material

Carbonates

Chemical

weathering

Acids, moisture

Introduction

Plants and crops are dependent on soil for the supply of water, nutrients and as a medium for growing. This dependence makes soil one of the most fundamental components for supporting life on the planet.

The term soluble salts refers to the inorganic soil constituents (ions) that are loosely bound to the matrix of soil and therefore can be dissolved in the water with relative ease.

The levels of soluble salts in the soil are important since high concentrations are considered an environmental stress and constitute a limiting factor for agriculture.

Furthermore some of the most important soil threats, such as salinisation and desertification are closely linked with increased concentrations of soluble salts.

Therefore, the determination of soluble salts in soils is crucial for the estimation of soil condition in relation to several soil threats and soil contamination.

Introduction

This study as a part of the compilation of the Geochemical Atlas of Cyprus project, aims to provide a detailed geochemical “snap shot” of the distribution and abundance of soluble salts in Cyprus soil.

For the purpose of this project an in-house method was developed for the extraction of soluble salts, following an optimized procedure.

Areas not under the effective control of the Government of the Republic of Cyprus

Sampling Method

Sample locations - determined by GPS.

The surface was cleared of recent organic debris.

Top soil samples (0–25 cm depth).

All samples were sieved to <2 mm.

Samples delivered and archived at the GSD.

Ion Chromatography

Eluent

Data Processing

Pump

Conductivity Detector

Guard Column

Separator Column

Suppressor

Trace

Method Development

Method Development

Sample Preparation:

sieving < 2 mm mesh size

milling

Experimental

5g sample / 200ml DW

120 minutes shaking

filtration (ashless filter paper)

conductivity measurement

filtration (0.45 μm membrane filter)

liquid chromatography

Samples of conductivity greater than 600μS/cm or with anion concentrations exceeding the calibration range were diluted.

Control:

CYP-A , a calcareous sediment collected from an outcrop of Pakhna.

Method Development

Distribution of Fluorides

Fluorine is the most abundant halogen in the earth’s crust.

It is the most electronegative element and binds metals forming complexes, which are adsorbed readily to the soil and plants.

Fluorine is phytotoxic, causing damage in vegetation, wildlife and humans.

Fluorine as an element in soil has a world average value of 200-300 mg/kg.

The main natural source of inorganic fluorides in soil is the parent rock. During weathering, some fluoride minerals are rapidly broken down.

Fertilizer application is the main nongeogenic source of fluoride ions and fluorapatite is an important calcium- and fluoride-containing mineral used as a source of phosphates in the fertilizer industry.

Phosphate fertilizers are manufactured from rock phosphates, which generally contain around 3.5% of fluorine.

Fluoride applied through fertilizer tends to have high residence time within the soil matrix particularly in soils of high clay content, high organic carbon content, high amorphous aluminium species or low pH.

F-

fluoride

Ion chromatography

34 E

33 E

Top soil

(0 – 25 cm)

Keryneia

Areas not under the effective

control of the Government

of the Republic of Cyprus

Lefkosia

500

Ammochostos

Polis

25

22

F-

(mg/kg)

35 N

20

19

Ayia Napa

18

16

14

12

Pafos

11

8

Lemesos

Distribution of Fluorides

LODreproducibility: 10 mg/kg

average value: 18.7 mg/kg

highest value: 3536 mg/kg

Distribution of Chlorides

The mantle, the crust and the oceans are the three main reservoirs of earth chlorine with only the oceanic chlorine being readily mobile.

Since parent materials in general contain only minor amounts of chloride, little of this nutrient arises from weathering.

Most of the chloride presents in soils arrives from rainfall, marine aerosols, volcanic emissions, irrigation waters, and fertilizers.

Chloride accumulates primarily in soil under arid conditions where leaching is minimal and where chloride moves upward in the soil profile in response to evapotranspiration .

Near the ocean, soils have high levels of chloride.

High chloride ion concentrations in soil, above geogenic concentrations, are often considered as a salinisation problem world wide and occur in warm and dry locations where soluble salts precipitate from water and accumulate in the soil.

Cl-

chloride

Ion chromatography

34 E

33 E

Top soil

(0 – 25 cm)

Keryneia

Areas not under the effective

control of the Government

of the Republic of Cyprus

Lefkosia

2,000

Ammochostos

450

Polis

350

270

35 N

230

200

Ayia Napa

180

160

Cl-

(mg/kg)

140

Pafos

120

80

Lemesos

Distribution of Chlorides

LODreproducibility: 149 mg/kg

average value: 809.3 mg/kg

highest value: 664778 mg/kg

The Nitrogen Cycle

http://www.physicalgeography.net

Distribution of Nitrates

Nitrate ions mainly originate from anthropogenic origins and constitute a very clear descriptor for characterising agricultural land use.

The main source of nitrates is the application of synthetic fertilizers or manure to fields.

Nitrate vulnerable zones (NVZ) have been designated by the Cyprus government through studies (Geological Survey Department, 2000) in an effort to comply with the Nitrate Directive (91/676/EEC).

The Directive has the objectives of reducing water pollution caused or induced by nitrates from agricultural sources and preventing further pollution.

220

150

100

80

70

55

40

32

NO3-

(mg/kg)

26

22

15

Distribution of Nitrates

NO3-

nitrate

Ion chromatography

34 E

33 E

Keryneia

P

ICP-MS

Top soil

(0 – 25 cm)

Keryneia

LODreproducibility: 12 g/kg

average value: 68.4 mg/kg

highest value: 3001 mg/kg

Areas not under the effective

control of the Government

of the Republic of Cyprus

Lefkosia

Lefkosia

Ammochostos

Ammochostos

Polis

Polis

35 N

Ayia Napa

Ayia Napa

Larnaca

Pafos

P

(%)

Lemesos

Pafos

Lemesos

0.160

0.100

0.092

0.085

0.062

0.055

0.042

0.035

0.025

0.020

0.010

Distribution of Sulfates

Sulfate ions are made available from dissolution of sulfate salts from oxidation of sulfur-bearing minerals in soils all around the world.

Among the sulfur-bearing minerals identified in sedimentary rocks, iron sulfide polymorphs, pyrite and marcasite, are the more common forms, of which pyrite is the most common. Oxidation of these sulfide groups releases sulfate phases into soils.

The soils that contain iron sulfide minerals or their oxidation products are known as Acid Sulfate Soils (ASS).

If the ASS are drained and exposed to air, the sulfides react with oxygen to form sulfuric acid which can create a variety of adverse impacts: killing vegetation and aquatic organisms, acidifying groundwater and water bodies, degrading concrete and steel structures to the point of failure.

750

300

180

140

120

100

80

65

SO42-

(mg/kg)

55

45

30

Distribution of Sulfates

SO42-

sulfate

Ion chromatography

34 E

33 E

Top soil

(0 – 25 cm)

Keryneia

S

XRF

LODreproducibility: 49 mg/kg

average value: 160.3 mg/kg

highest value: 231701 mg/kg

Keryneia

Areas not under the effective

control of the Government

of the Republic of Cyprus

Lefkosia

Lefkosia

Ammochostos

Polis

Ammochostos

Polis

35 N

Ayia Napa

Ayia Napa

Larnaca

Pafos

Lemesos

S

(mg/kg)

Pafos

100,000

Lemesos

6000

1500

10,000

1200

S

XRF

(mg/kg)

1000

900

1,000

800

700

500

100

400

SO42-

ion chrom

(mg/kg)

300

200

10

10

100

1,000

10,000

100,000

F-

fluoride

NO3-

nitrate

Cl-

chloride

SO42-

sulfate

34 E

34 E

34 E

34 E

33 E

Top soil

(0 – 25 cm)

33 E

33 E

33 E

Keryneia

Top soil

(0 – 25 cm)

Top soil

(0 – 25 cm)

Top soil

(0 – 25 cm)

Keryneia

Keryneia

Keryneia

Lefkosia

Lefkosia

Lefkosia

Lefkosia

Ammochostos

Ammochostos

Ammochostos

Ammochostos

Polis

Polis

Polis

Polis

35 N

35 N

35 N

35 N

Ayia Napa

Ayia Napa

Ayia Napa

Ayia Napa

Pafos

Pafos

Pafos

Pafos

Lemesos

Lemesos

Lemesos

Lemesos

Distribution of Soluble Salts

Conclusions

The soluble salt distribution maps provide the baseline values for every geological formation of the island of Cyprus and give sufficient information of soil contamination sides.

The two salt lakes of the island are considered to be the main non-anthropogenic contamination sources resulting to enhance values of all the measured soluble salts and particularly those of the chlorides and sulfates.

The soluble salt distribution maps confirms also the anthropogenic soil contamination with nitrates and sulfates due to fertilizers application and mining activity respectively.

This study provides a basis for a number of future projects dealing with environmental monitoring and management.

The observed soil contamination caused by mining activity gives also the opportunity to run several mine rehabilitation projects in Cyprus.